Scholars have long assumed that as workers spend more time at work fewer hours are available for their non-work lives leading to negative effects in both domains, and most studies examining the impact of work hours on work and life domains have supported this viewpoint. However, the majority of these studies have used one-dimensional measures of work-family conflict (WFC) and family-work conflict (FWC) on homogenous samples which included primarily married managers and professionals with children. Further, despite calls to examine non-linear relationships between work hours and WFC and FWC, few studies have done so. This study uses multi-dimensional measures to examine the linear and non-linear (quadratic) effects of work hours on WFC and FWC in a heterogeneous sample and examines the moderating effects of several work and family characteristics on these relationships. The findings indicate that whereas work hours have a linear relationship with WFC, the relationship between work hours and FWC is curvilinear. Managerial support was found to moderate the relationship between work hours and one dimension of FWC. Number of children moderated the relationships between work hours and WFC and another dimension of FWC. (Contains 3 figures and 3 tables.)